COURSE: Detailed Explanation on Entropy Questions Lesson : Questions -(1-3)

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Question 1 On the basis of the first law fill in the blank spaces in the following table of imaginary heat engine cycles. On the basis of the second law classify each cycle as reversible, irreversible, or impossible Cycle Temperature Rate of Heat FlowRate of Efficiency work Source SinkSupplyRejectionOutput (a) 327 C 27 C 420 kJls 230 kJls .kVW (b) 1000 C 100oC ..kJ/min 4.2 MJ/min kW 65% 65% (c) 750 K 300 K ...kJ/s kJ/s | 26 kW | (d) 700 K300 K2500...kcal/h1 kW kcal/h

Solution 1 Cycle Temperature Rate of Heat Flow Rate of Effici- Remark work enc Supply Sink 27 C Rejection 230 kJ/s max 50% rrev.possible Source (a) 327 C 420 kJ/s 190kW0.4523 (b)1000 C 100 C 12000 kJ/km max=70.7% irrev.possible 4.2 kJ/m 7800 kW | 65% ma,-60% rev. possible 750 K 300 K 43.33 kJ/s | 17.33 kJ/s | 26 kW | 60% 2500 kcal/h 1640 kcal/h (d)700 K 300 K 1 kW 4.4% irrev.possible

Question 2 The latent heat of fusion of water at 0 C is 335 kJ/kg. How much does the entropy of 1 kg of ice change as it melts into water in each of the following ways: (a) Heat is supplied reversibly to a mixture of ice and water at 0 C. (b) A mixture of ice and water at 0 C is stirred by a paddle wheel

Solution 2 (a) (AS) system - + 1x335 kJl HK Ice Water 273 K - 1.227 kJ/K (b) (AS) system 273 0 273

Question 3 Two kg of water at 80 C are mixed adiabatically with 3 kg of water at 30 C in a constant pressure process of 1 atmosphere. Find the increase in the entropy of the total mass of water due to the mixing process (cp of water4.187 kJ/kg K)

Solution 3 If final temperature of mixing is Tr then 2x (353-T) 2 kg 3 kg -3>< ( -303) 80 C 353 K30 C 303 K or T323 K (AS) system (AS)I (AS) Iu 323 323 303 32 +3 x4.187 x In 303 353 323 - 2 x 4.187 In 0.05915 kJ/K

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Harshit Aggarwal

Cleared UPSC ESE twice with Rank 63 and 90 in mechanical engg. Got 99 percentile in GATE. Cracked ONGC, BHEL,ISRO, SAIL, GAIL successfully

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Riya Thakur

2 months ago

okay i got the correct ans yes mam there r 5 gates

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Rafiq n

14 days ago

temp is same..

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Suraj prasad singh

2 months ago

how the mixture of ice and water when stirred by paddle entropy is zero

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